The present invention relates to a wire bonding machine that can be used or assembling semiconductor devices and a wide range of electric and electronic components, and in particular to a bonding head which is suitable for use in high speed wire bonding machines and single-point TAB bonding machines.
The bonding head of a wire bonding machine generally comprises a carriage block which is adapted to be moved both laterally and vertically so as to be moved to a desired location over the work piece such as a semiconductor device or circuit board, and a transducer block which carries a bonding tool and is supported by the carriage block so as to selectively apply the bonding tool onto a desired point on the work piece. When applying the bonding tool onto a desired point on the work piece, it is desirable to move the bonding tool vertically without involving any lateral movement as much as possible. The lateral motion of the bonding tool as it engages a work piece is called as xe2x80x9ctip skidxe2x80x9d, and could impair the bonding quality.
FIG. 6 shows a conventional wire bonding head comprising a horizontally extending transducer block 1 which is pivotally attached to a carriage block 2 at its base end via a horizontal pivot 3. The transducer block 1 comprises a tool holder 4 incorporating a transducer (not shown in the drawing) for converting electric energy into ultrasonic vibration energy, a horn 5 extending from the free end of the holder 4 and functionally connected to the transducer, and a vertically extending bonding tool 6 attached to the free end of the horn 5 by a tool set screw 8. The bonding tool 6 engages a work piece at its tip 7 to accomplish the known ultrasonic bonding process.
The base end of the transducer block 1 is provided with a vertical arm 1b which engages a stopper 10 provided in the carriage block 2 to define the limit of the downward pivotal movement of the transducer block 1 around the pivot 3. A linear motor 9 is provided between an intermediate part of the vertical arm 1b and the carriage block 2 to actuate the pivotal movement of the transducer block 1 around the pivot 3.
The lateral movement of the tip 7 of the bonding tool 6 or tip skid can be minimized by selecting the position of the pivot 3 at a substantially same vertical level as the bonding tool tip 7, and increasing the distance between the pivot 3 and the bonding tool tip 7. Therefore, the transducer block 1 typically consists of an elongated arm extending horizontally. This arrangement has the advantage of simplicity.
However, according to this arrangement, because the position of the pivotal joint (pivot 3) between the transducer block 1 and the carriage block 2 is relatively low, it is difficult to avoid the interference between the pivotal joint and the work piece. Therefore, the area of the work piece that can be covered by the bonding head may be limited, and the restriction on the size and shape of the pivotal joint puts a severe restriction on the design of the bonding head.
It is also possible to use a pair of parallel sheet springs to support the transducer block on the carriage block. The parallel sheet springs enable the transducer block to move linearly, and the bonding tool tip may be guided so as to move vertically substantially without any lateral movement. In this case, the parallel sheet springs serving as the pivotal joint between the transducer block and the carriage block may be provided at a certain height, and the interference with the pivotal joint and the work piece can be avoided.
However, this arrangement increases the complexity of the bonding head. More importantly, as the transducer block moves vertically, it involves a significant inertia because the transducer undergoes a purely translational motion instead of a pivotal movement. The bonding tool is required to engage onto and disengage from the work piece at high speed, and the large inertia of the transducer block tends to cause a severe impact on the work piece. Such a large impact causes an excessive-plastic deformation of the work piece, and this tends to impair the bonding quality. It is thus desired to minimize the effective mass of the transducer block as much as possible, particularly when the speed of the movement of the bonding tool is desired to be maximized.
In view of such problems of the prior art, a primary object of the present invention is to provide a wire bonding head which allows the bonding tool tip to move vertically substantially without any lateral movement so as to achieve a high bonding quality.
A second object of the present invention is to provide a wire bonding head which can minimize the effective inertia of its transducer block, and can thereby achieve a high bonding quality.
A third object of the present invention is to provided a wire bonding head which can minimize the effective inertia of its transducer block, and can thereby operate at high speed.
A fourth object of the present invention is to provided a wire bonding head which is simple in structure, and is relatively free from plays.
According to the present invention, these objects can be accomplished by providing a wire bonding head, comprising: a carriage block adapted to be moved to a desired location over a work piece, and having a first end and a second end which is laterally displaced from the first end; a main link member having a first end pivotally attached to the first end of the carriage block via a first pivot having a pivot axis extending substantially horizontally and perpendicularly with respect to a line extending between the first and second ends of the carriage block; a transducer block having a first end carrying a bonding tool and a second end which is laterally displaced from the first end of the transducer block, a second end of the main link member being pivotally connected to the transducer block via a second pivot having a pivot axis extending in parallel with the pivot axis of the first pivot and, preferably, substantially through a gravitational center of the transducer block; an actuator for selectively causing an angular movement to the main link member around the first pivot; and a coupling joint connected between the second end of the carriage block and the second end of the transducer block which is constrained so as to create a lateral movement of the second end of the transducer block that is required to move a bonding tool tip vertically and linearly as the transducer block is moved vertically relative to the carriage block by the main link member via the second pivot.
The bonding tool tip is thus enabled to move along a vertical and linear path as the transducer block moves toward and away from the carriage block. Because the carriage block essentially undergoes a pivotal motion around the first pivot, the effective inertia of the transducer block is kept small as compared to the case of causing a translational motion to the transducer block. The structure according to the present invention is relatively simple and low in cost, and can be made free from plays particularly when the pivots consist of spring pivots using flexures.
According to a preferred embodiment of the present invention, the coupling joint comprises a substantially vertically extending secondary link member having a first end pivotally connected to the second end of the transducer block via a third pivot, and a second end pivotally connected to the second end of the carriage block via a fourth pivot. Also, the first pivot and bonding tool tip are preferably located at a substantially same lateral position, and the first and third pins are preferably located at a substantially same height.
Alternatively, the coupling joint may comprise a slider guided horizontally along the second end of the carriage block, and an arm extending from the second end of the transducer block and having a free end pivotally attached to the slider via a slider pivot. Preferably, the slider pivot is located at a substantially same height as the first pivot, and the second pivot is located at a mid point in a line extending between the bonding tool tip and the slider pivot. Preferably, the first pivot and bonding tool tip are located symmetric with respect to a horizontal line passing through the second pivot so as to form the Scott-Russel link mechanism.
A wide range of actuators can be used for producing a relative movement between the carriage block and the transducer block. According to a preferred embodiment, the actuator consists of a linear motor interposed between the main link member and the carriage block.
To achievie a same goal, the coupling joint may also be connected between the carriage block, the main link member and the transducer block, the coupling joint being constrained so as to cause a rotation of the transducer block by a substantially same but opposite rotational angle as that of the main link member with respect to the carriage block. In this case, the coupling joint preferably comprises a pair of fixed gears fixedly attached to the transducer block and carriage block, respectively, and a third gear rotatably supported by the main link member and meshing with both of the fixed gears, the gear fixed to the carriage block having a radius twice that of the gear fixed to the transducer block.